19 Oct 2021

The lowdown on rapid antigen tests

From The Detail, 5:00 am on 19 October 2021
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As we speak, hundreds of thousands of rapid antigen Covid -19 tests are winging their way to New Zealand. 

Last week, a collective of businesses were given the green light to import more than 300,000 test kits into the country, following a long-running lobbying effort.

It's the first time these tests will be used at scale by private businesses.

But rapid antigen tests are common overseas: in the UK, they're provided to anyone who wants one, free of charge. 

So what are rapid antigen tests? How do they differ from the nasal or throat swab PCR tests we currently use? Why have they taken so long to reach our shores in bulk, and what will the future of Covid testing in New Zealand look like, as we continue down the suppression route? 

On today's episode of The Detail, Emile Donovan speaks to Professor Michael Plank from Te Pūnaha Matatini and Dr Lesley Gray, a senior lecturer in the University of Otago’s department of public health, about the past, present and future of Covid testing in Aotearoa.  

Of the three types of testing to diagnose Covid-19 in someone - nasal and throat PCR tests, saliva PCR tests, and rapid antigen tests - there are clear advantages and disadvantages to each.

Nasal or throat PCR tests are expensive and resource-intensive, and because they have to be analysed in a lab, can take a long time to deliver a result - usually a couple of days. 

Saliva tests are reliable, but expensive, take a long time, and aren't currently used at scale in New Zealand, embroiled as they are in something of a bureaucratic purgatory.

Rapid antigen tests, on the other hand, are nimble: they still involve a throat or nasal swab, but they deliver a result in as little as 15 minutes, and can be used by just about anyone, any time, anywhere.

On the other hand, they aren't as reliable as PCR tests: when administered by a trained medical professional, their reliability is around 75-90 percent; but when used by an untrained person, that accuracy can drop as low as 50 percent.

When New Zealand was pursuing an elimination strategy, it made sense to stick with PCR testing, says Dr Gray.

But now that we've accepted there will be at least some community transmission of Covid, rapid antigen tests do have a part to play, particularly as a sort of screening tool for people who are travelling a lot for work (for example truck drivers).

Rapid antigen tests have been utilised in some countries to allow people to enjoy greater freedoms: at a concert in Barcelona back in March, a negative rapid antigen test was a condition of entry.

But Gray warns against seeing them as a silver bullet: she says these tests are a tool which can help complement PCR testing, but certainly isn't a substitute for it.

She says as New Zealand continues along its suppression strategy, more widespread and more regular testing is likely to become a part of everyday life, and Aotearoa should be using all the tools at its disposal to help with that.


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